Method for hydroelectrometallurgy

ABSTRACT

A hydroelectrometallurgy method comprising suspending particles of a crude metal or metal sulfide in the anode zone and seed particles of pure metal in the cathode zone, causing such particles to collide with the surfaces of the anode and cathode, respectively, and thereby effecting the corresponding electrochemical reaction on each of the particles, whereby metal ions are formed in the anode zone and the seed particles grow into coarse particles in the cathode zone as the result of precipitation of the metal thereon. According to this method, since the total surface area of the particle is very large, a greater electric current can be applied as compared with the conventional electrolytical refining or winning method, and the manufacturing rate of pure metal can be increased greatly.

lfiametani Jan. 22, 1974 METHOD FOR HYDROELECTROMETALLURGY [75] Inventor: Hiroshi Kametani, Hatogaya, Japan [73] Assignee: Director of National Rwearch Institute for Metals, Tokyo, Japan [22] Filed: Feb. 3, 1971 [21] Appl. No.: 112,180

[52] US. Cl 204/1 R, 204/107, 204/108, 204/112, 204/113, 204/117, 204/118,

204/119, 204/ 120, 204/122, 204/DIG. 10

[51] Int. Cl. C22d 1/16, C22d 1/14, C22d 1/18 [58] Field 01Search.... 204/106, 108, 107, 112-113, 204/117-118, l19-120, 122, 261, 263,1R

[56] References Cited UNITED STATES PATENTS 2,761,829 9/1956 Dolloff 204/106 BLAST FURNACE WHITE METAL 2 PULVERIZATION 3 AND GRINDING Primary ExaminerJohn H. Mack Assistant Examiner-Richard L. Andrews Attorney, Agent, or Firm-Sherman and Shalloway [57] ABSTRACT A hydroelectrometallurgy method comprising suspending particles of a crude metal or metal sulfide in the anode zone and seed particles of pure metal in the cathode zone, causing such particles to collide with the surfaces of the anode and cathode, respectively, and thereby effecting the corresponding electrochemical reaction on each of the particles, whereby metal ions are formed in the anode zone and the seed particles grow into coarse particles in the cathode zone as the result of precipitation of the metal thereon. According to this method, since the total surface area of the particle is very large, a greater electric current can be applied as compared with the conventional electrolytical refining or winning method, and the manufacturing rate of pure metal can be increased greatly.

9 Claims, 5 Drawing Figures SEED F I [.T RATION RESIDUE SHEET 1' [1F 4 Fig] AIR 2) CoPPER CONCENTRATE SILICA SULFUR DIOXIDE GAS WHITE BLAST FURNACE PULVERIZATION AND GRINDING sLuRRY 4 ANODE CATHODE ELECTROLYTIC 5 CELL CLARIFYI NG STEP ZONE SEED PARTICLES WASHING AND DEHYDRATION IPRCDLICTI FILTRATION RESIDUE PATENTEU QE '1' IO L49 PRODUCT SHEET 2 OF 4 STARTING HQRTICLES Hg. 3 IMPURITIES M LES I PARTICLES METHOD FOR HYDROELECTROMETALLURGY This invention relates to a novel method for hydroelectrometallurgy. More specifically, the invention relates to a method for conducting the refining or winning of metals by utilizing electrochemical reactions occuring on the surfaces of particles of metallic materials suspended in an electrolyte.

Electrolytic refining and electrolytic winning have been heretofore conducted broadly in the art of hydroelectrometallurgy. The former is a method comprising carrying out an aqueous solution electrolysis with use of a crude metal containing impurities as an anode and 'thereby precipitating a pure metal on a cathode. The

latter is a method comprising carrying out the electrolysis by employing as the electrolyte a solution in which a metal has been dissolved in advance in the form of an ion, thereby precipitating the metal on a cathode and collecting the same.

Conventional processes for recovering pure metals from starting metal ores by hydroelectrometallurgy comprise a variety of complicated steps. By way of example, a process for the manufacture of copper from a copper sulfide ore will now be explained. This process comprises steps of melting a copper concentrate from a copper sulfide ore in a blast furnace to thereby convert the concentrate to a sulfide containing copper and iron, so-called matte (Cu SFeS); transporting the matte to a converter, blowing air thereinto and removing the iron to thereby convert the matte to copper sulfide, so-called white metal" (Cu S); further blowing air into the white metal to convert it to blister copper;

' removing a majority of impurities remaining in the blister copper; transporting the blister copper to a refining furnace where it is reduced to remove the excessive oxygen; casting the resulting crude copper into anodes; and conducting the electrolysis with use of these anodes to obtain pure copper.

in such complicated conventional refining processes, there is a limit when improvement of the refining efficiency or lowering of the manufacturing cost is intended or tried by improving individual steps. For instance, in the electrolytic refining, a great deal of labor and equipment are required for manufacturing crude copper anode plates and starting cathode plates, insertion of anode and cathode plates into an electrolytic cell, withdrawal of these plates from the cell, washing of these plates, prevention of occurrence of a short cut between these plates and investigation of the operation. This is also a fatal defect of other metal refining processes.

Another defect of conventional hydroelectrometallurgy methods is that a satisfactorily high rate of the electrolysis cannot be attained. In the conventional industrial electrolysis, plateJike anodes and cathodes are hung vertically in an electrolytic cell alternately with a distance of several centimeters to 15 cm or more, and the electrolysis is effected by passing of a current of a limited low current density of less than 3 amperes per dm When the current density is increased in order to attain a high rate of electrolysis, as is well-known in the art, twig-like metal crystals (dendrites) grow on the surfaces of electrodes and thus a short cut occurs between the anode and cathode, with the result that it is impossible to continue the electrolysis. Particularly because the distance between every two electrodes is very short as described above, occurrence of the short cut is frequent. Formation or growth of the above dendrites can be inhibited to some extent by adding a suitable agent to an electrolyte or adjusting other operation conditions, but no method has not been known of completely preventing formation or growth of dendrites on the surfaces of electrodes. Accordingly, the problem of increasing the electrolysis rate has been heretofore solved by increasing the number of electrolytic cells, in other words, expanding the electrolysis area. Consequently, in the art of the metal refining, an area required for the electrolysis occupies a great part of the site of the plant.

This invention is based on a novel technical concept quite different from the technical concept of the conventional art and can overcome the above-mentioned defects of the conventional methods by suspending particles of the starting metal materials in an electrolytic solution and effecting the electrolysis on the surfaces of the particles. In accordance with this invention, the electrolysis efficiency per unit area can be made more than 10 times as high as in the conventional methods and, therefore, the electrolysis rate can be greatly increased. Furthermore, charging of starting metal particles and recovery of product metal particles can be accomplished automatically. This invention will be detailed hereinbelow.

In accordance with this invention, a method of hydroelectrometallurgy is provided which comprises suspending in an electrolytic solution particles of a starting metallic material selected from a crude metal and a metal sulfide in the neighborhood of an anode and seed particles of the pure metal in the neighbourhood of a cathode, and while passing an electric current between the two electrodes, causing the two kinds of particles to collide with the surfaces of the anode and cathode, respectively, thereby effecting the corresponding electrochemical reaction on the particles which have been loaded with positive electric charge and negative electric charge, respectively, as the result of the collision.

Electrodes are dipped in an electrolytic solution and, when metallic particles are added into the solution and agitation is carried out, particles are suspended in the solution and are allowed to move in the solution de pending on the movement of the solution caused by the agitation. At a certain moment the particles collide with an electrode while they are allowed to move. When the electrode is imprinted with a positive or negative electric charge, the particles, upon collision with the electrode, are electrically charged with almost the same voltage. The next moment the particles move away from the electrode but since they have already been loaded with the electric charge, the electrochemical reaction proceeds between the particles and the surrounding solution. As the particles are not electrically connected with a cable, they gradually lose their electric charge in proportion to the advance of the reaction and finally their voltage reaches a certain level. However, the particles are given a chance of colliding with the electrode again by the agitation and then the above procedures are repeated. Thus the electrolytical reactions are allowed to continue as a whole.

Upon collision with an anode, particles of a crude metal or a metal sulfide give electrons to the anode and are positive charged. Thus, in the particles suspended in the electrolytic solution an anodic reaction expressed by the formula (I) or (1) whereby they lose their charge. At the next collision the particles receive a negative charge from the cathode again and the same procedures are repeated.

In the above reaction formulas (l), (l') and (2), M

stands for a divalent crude metal, MS stands for a sulfide of a divalent metal, S represents elementary sulfur, 2 indicates one electron, M stands for a divalent metal ion and M is a precipitated, pure divalent metal.

As the result of the above reactions, metal ions are formed from the metallic material in the anode zone and growth of the precipitated metal advances on the particles of the pure metal in the cathode zone. In the anode zone, in addition to the dissolution of the metallic material formation of a gas and oxidation of ions of impurities in certain cases simultaneously occurs.

As described above, in this invention corresponding electrochemical reactions occur on the surfaces of particles suspended in anode and cathode zones, respectively. The surface area of these particles can be made much larger than the surface area of electrode plates used in the conventional methods. Accordingly, a much greater electric current can be applied at the same current density as that maintained on the conventional electrode plate. For instance, in this invention it is easy to apply an electric current more than times as great as in the conventional methods while maintaining the current density at the same level. Consequently, it is possible in this invention to attain an extremely high electrolysis rate.

The above-mentioned method of this invention can be worked continuously and automatically. In this case, starting crude metallic particles are continuously fed in the form of solids or slurry into the anode zone and impurities derived therefrom are continuously discharged, while fine particles (seed particles) of the pure metal are continuously fed to the cathode zone and enlarged particles of the pure metal grown by the electrolysis are continuously recovered as product. Since valuable metal ions are contained in the solution of impurities withdrawn from the anode zone, the solution is subjected to a conventional treatment for removal of the impurities and then his recycled and reused as the electrolytic solution.

The main advantages of the method of this invention are summarized below:

a. Not only crude metals but also naturally occurring metal sulfides can be used as the starting material.

b. Complicated steps adopted in the conventional extractive metallurgy starting from metal ores can be omitted or simplified, whereby the manufacturing cost can be greatly reduced. For instance, the method of this invention does not require any step of cast molding anode plates of a crude metal, and the material to be electrolyzed can be used in the granule form.

0. Since the granular material having a great surface area can be used as the starting material, a great current can be applied in the method of this invention. In other words, a high electrolysis rate can be attained with use of a small size of an electrolytic cell. Furthermore, the heat generated by such high rate electrolysis can be effectively utilized and the process may be operated at high temperatures, with the result that the electrolysis efficiency can be further increased.

(1. Since the equipment can be made compact and a great current can be applied, the separation of ions of impurities by the anodic oxidation can be accomplished very effectively. In the method of this invention it is unnecessary to use expensive oxidants which must be inevitably used in the conventional methods for removing impurities such as iron, manganese, arsenic and antimony.

e. When formation of a gas accompanies the anodic reaction, use of a compact, closed apparatus and application of a great current make it possible to catch and collect the gas concentrically with ease. In the conventional electrolytic cell of an open type it is impossible to avoid formation of gas bubbles, splashing of the electrolytic solution caused by breakage of gas bubbles, contamination of air caused by the splashing of the electrolytic solution, and the resulting worsening of the environment.

f. The operation can be conducted continuously and automatically, whereby the manufacturing efficiency of pure metal end products can be greatly increased. For instance, the method of this invention does not require a troublesome step such as the exchange of electrodes which is necessary in conventional methods.

Preferable embodiments of the practice of this invention will now be explained.

In this invention, electrodes are only for receipt and delivery of electrons from and to metallic particles suspended in the electrolytic solution, and the electrodes are not consumed by the electrolysis or no metal is deposited on them during the electrolysis. Accordingly, no critical limitation is imposed on the material constituting the electrode. In general, however, it is preferred that the electrode is made up of the same metal as that to be recovered by the electrolysis.

The size of the starting metallic particles and the seed metal particles to be used in this invention is such that the particles can maintain the suspension state in the electrolytic solution, and it is suitably decided depending on the kind of means imparting vibration to the solution. In general, however, the metallic particles of a size of-l50 mesh and the seed particles of a size of larger than 50 microns are preferably used.

The metallic particles are suspended in the electrolytic solution by any optional method. For instance, suspension is attained by rotation of an ordinary stirrer, vertical movement of a perforated plate or shaking of the electrolytic cell per se. It is also possible to suspend the particles in the electrolytic solution by adopting a fluidi zedsystem flowing the electrolytic solution.

In this invention particles in the anode zone and particles in the cathode zone should not contact each other. The contact will be prevented most simply by provision of a diaphragm between the two electrodes.

When particles in the anode zone are those of a metal sulfide which has a low electric conductivity, in order to facilitate the delivery and receipt of electrons between the particles and electrodes it is possible provide in the electrolytic solution a vehicle conveying electrons between the particles and electrodes. 'As such vehicle, so called electron carrier, ions of valencychangeable metals are preferably used. For instance, iron ions which can be present in either divalent or trivalent state are effectively used. The iron ion can be converted to the trivalent state from the divalent state and vice versa, as illustrated in the following reaction formula:

lnstead of the valency-changeable metal ion, powders of electroconductive substances insoluble in the electrolytic solution, such as lead, aluminum, and stainless steel may be used. The receipt and delivery of electrons can be promoted by the presence of such metal powders suspended in the electrolytic solution together with particles of the starting metal sulfide. The transfer of electrons between such electroconductive powders and the anode can be conducted very easily, and the powders perform the same action as that of the anode. Consequently, the substantial area of the electrodes can be increased very greatly and the chance of the collision of the starting metallic particles with the anodes can be increased proportionally. Thus, any trouble due to insuficient conductivity can be avoided.

Also in order to increase the chance of collision of the starting metallic particles with the electrodes, it is possible to use electrodes of a great surface area, e.g., electrodes of a net-like structure.

In the vicinity of the anode zone, the starting material containing impurities is suspended, and the solution in this zone contains impurities at higher concentrations. Accordingly, in order to obtain the pure metal in the cathode zone, it is desirable to prevent the solution in the anode zone from shifting from the anode zone to the cathode zone and to keep the solution in the cath ode zone in the clean state. For attaining this purpose it is sufficient to maintain the anode side at a little lower pressure than on the cathode side (based on the hydrostatic pressure) with the diaphragm being a boundary and to allow the solution in the cathode zone to flow toward the anode through the diaphragm gradually but continuously. The difference of the hydrostatic pressure between both zones can be easily brought about by adjusting the height of the free level of the solution suitably in both zones.

All the metals that are objects of the conventional hydroelectrometallurgy can be applied to the method of this invention and good results are obtained. More specifically, metals exhibiting a standard electrode potential exceeding 1 volt (at 25C.) such as zinc, iron, cobalt, nickel, tin, lead and copper are applicable to the method of this invention.

The process for recovering pure copper from copper sulfide according to this invention and some embodiments of the apparatus for use in practising the hydro electrometallurgy method of this invention will now be detailed by referring to accompanying drawings.

in the drawings,

FIG. 1 is a flow diagram illustrating the continuous process starting from copper sulfide concentrate obtained by mineral dressing of a copper sulfide ore and recovering a pure copper product by utilizing the method of this invention;

FIG. 2 is a side view illustrating the section of one embodiment of the electrolytic cell used in the hydroelectrometallurgy method according to this invention;

FIG. 3 is a flow diagram illustrating steps of one embodiment of the continuous process according to this invention; g H A FIG. 4 is a side view illustrating an embodiment of the metal electrolysis apparatus of a pile type used for practising this invention; and

Copper concentrate is heated at about 1,300C. together with silica in a blast furnace while feeding a sufficient amount of oxygen and converted to white metal (consisting of percent of copper and remaining sulfur and other minor impurities). The excessive sulfur is discharged in the form of sulfurous acid gas and a majority of iron is contained in the slag in the form of oxides. White metal 2 formed in the blast furnace 1 is flown to the outside continuously or intermittently depending on the size of the furnace, and it is cooled and solidified, for instance, by pouring it into flowing water.

.The white metal which has been rapidly cooled by such a method is britle and is easily pulverized by ball milling. The resulting ground white metal 3 is converted to a slurry 4 by utilizing a part of the liquor discharged from the anode zone 6 of an electrolytic cell or employing the starting electrolytic solution. Then the slurry is introduced into the electrolytic cell 5 by means of a pump or the like. In order to promote the anodic reaction, it is desirable that the white metal particles have a size not exceeding mesh. Also it is preferred that the concentration of the slurry is as high as possible within a range causing no disadvantage in the operation. The electrolytic cell 5 is divided into anode zone 6 and cathode zone 7 with a diaphragm 12 being a boundary. The white metal particles contained in the slurry introduced into the anode zone undergo the above-explained anodic reaction and copper contained in the particles is dissolved in the electrolyte. Thus the concentration of Cu in the electrolytic solution is increased. in the case of the continuous process, however, since a catholyte of a low Cu concentration is continuously fed to the anode zone, the Cu formed by the anodic reaction is continuously withdrawn in the form contained in the electrolyte of a high Cu concentration, and therefore, the concentration of the Cu is maintained at a constant level in the electrolyte in the anode zone.

The insoluble residue containing impurities once contained in the starting white metal and the residue of the unreacted white metal appear in the anode zone. The particles constituting these residues have, in general, a finer size than the particles of the starting white metal contained in the slurry. Accordingly, the rising electrolyte to be discharged contains only the fine particles of the residues and they are continuously discharged from the anode zone in the state suspended in the electrolyte, whereas heavier particles of the starting white metal remain in the anode zone and undergo the anodic reaction. The suspension thus withdrawn from the anode zone is introduced to the clarifying step 8, though a part of the suspension is sometimes used for formation of a slurry of the starting white metal particles. In the clarifying step 8 the suspension from the anode zone is separated into the residual solid and the clarified solution by filtration. During this step the following particle-coarsening method may be adopted in order to facilitate the filtration and to separate the residual solid into individual components.

In the electrolyte discharged from the anode zone free sulfur formed by the anodic reaction expressed by above formula (1) is present. When the discharged liquor is heated at a temperature exceeding 1 19C., i.e., the melting point of sulfur, the free sulfur is melted to form droplets of liquid sulfur in the liquor. These droplets adhere to one another and grow into larger liquid drops. Accordingly, when the liquid is cooled again, coarse particles are obtained which can be separated very easily by filtration. During the above-mentioned growth of sulfur droplets, particles easily wettable with liquid sulfur, such as particles of the unreacted white metal, are caught in the drops of liquid sulfur and they can be easily separated from particles of lead sulfate, hydroxides and the like, which are difficultly wettable with liquid sulfur. Accordingly, when the liquid which has been subjected to the above particle-coarsening treatment is filtered so as to separate coarse particles and fine particles, two residues are obtained which differ with respect to their constituents. Each of these residues is subjected to the refining step by a suitable method and valuable substances such as gold, silver, bismuth and lead are recovered therefrom.

Generally, a small amount of iron is contained in the white metal, and this iron is oxidized in the anode zone together with copper and dissolved into the electrolytic solution in the anode zone, a greater part of which is present in the Fe state and a minor part of which is present in the Fe state. As explained, with respect to the reaction of formula 3, these iron ions are useful for conducting the anodic reaction effectively. in short, since the white metal contains a small amount of iron, an advantage is brought about that the anodic reaction is effectively allowed to advance without adding an iron salt from the outside of the system. In the continuous process, however, the electrolytic solution is always circulated, and it is necessary to remove the ferric ion present in the solution during the clarifying step, because the concentration of the iron ions as a whole is increased in the solution by their accumulation and because the presence of the ferric ion adversely influences the cathodic reaction. The removal of the ferric ions can be accomplished effectively by the following two methods. One method utilizes the hydrolysis reaction. According to this method, the ferric ion hydrolyzed to ferric hydroxide and the precipitate of ferric hydroxide is separated and removed by filtration. The removal by this method can be easily performed by increasing either or both the pH and temperature of the solution. The other method comprises adding a small amount of white metal particles to the solution withdrawn from the anode zone to thereby reduce the ferric ion to the ferrous ion. By adopting a combination of these two methods it is possible to maintain the ferric ion concentration in the solution fed to the cathode zone at a low level while preventing the accumulation of iron and to keep the ferrous ion concentration at a constant level not exceeding about grams per liter. The ferrous ion concentration is decided mainly depending on the residuence time of the white metal particles in the anode zone, the degree of the air oxidation naturally caused during the steps of pulverization, grinding and slurry-production, and the allowance of lowering in the electric current efficiency. In the hydroelectrometallurgy method according to this invention, since the anode zone and cathode zone are separated from each other by the diaphragm and the electrolysis is conducted in a closed apparatus without contact with air, the presence of the ferrous ion does not adversely affect the precipitation of copper on the cathode.

In addition to the above-mentioned methods, the clarifying step includes the following wet treatments, namely (a) the treatment for removal of solutes preventing the electrolysis in the cathode zone, (b) the treatment for removal of solutes which are easily incorporated in precipitated copper and lower the quality of the product copper, c) the treatment for preventing accumulation of sulfuric acid formed by the partial oxidation of sulfur contained in the white metal, and (d) the treatment for removal of solutes which do not directly concern the electrolysis but are accumulated in the circulated electrolytic solution.

These treatments may be suitably conducted depending on the kinds and amounts of impurities contained in the white metal, and the objects of these treatments can be attained by suitably combining known techniques customarily adopted in the art.

The solution of a high Cu concentration from which harmful components have been removed by the above-mentioned methods is continuously fed to the cathode zone 7 of the electrolytic cell 5 partially directly and partially through the particle-classifying step which will be described hereinafter.

Seed particles prepared in advance are fed continuously to the cathode zone, and undergo the cathodic reaction expressed by above formula 2, by which copper is precipitated on the surface of the seed particles. Thus the precipitation advances and the size of the particles is increased. The resulting coarse particles 10 fall down by gravity against the upward flow of the electrolytic solution fed to the cathode zone from the clarifying step, and they are separated from ungrown fine particles and are continuously withdrawn from the cathode zone. Then the withdrawn coarse particles pass through the washing and water-removing steps 11 and are recovered in the form of a product.

In order to prevent the precipitation or deposition of copper on the surface of the cathode plate and to allow the precipitation and growth of copper only on the particle surface, it is necessary to conduct the agitation in the cathode zone in a suitable manner depending on the size of the particles. It is difficult to maintain the stable suspended state in the solution containing a variety of particles differring greatly in particle size in the cathode zone of only one electrolytic cell only by an agitation condition. Accordingly, in order to increase the yield of the product with use of a smaller amount of seed particles, namely to grow seed particles into particles as large as possible, it is suitable to conduct the continuous electrolysis by using a plurality of electrolytic cells, passing the particles continuously through these cells in succession according to degree of the growth of the particles and adopting suitable varying agitation conditions in each cell depending on the size of the particles passing through it.

In the cathode zone, the electrolytic solution of a high Cu concentration flows from the clarifying step 8 and the catholyte of a low Cu concentration is withdrawn. A part of the catholyte is shifted directly to the anode zone through the diaphragm because of the hydrostatic pressure, but the remainder is fed -to the anode zone by means of a pump or the like.

The above continuous process has been explained by referring to the refining of copper, but the principle of the above continuous process may be applied to the refining of other metals. For instance, in the case of a lead sulfide concentrate, since the concentrate has a relatively high lead content and is rich in reactivity, it may be directly converted to a slurry 4 without passing through the blast furnace l and the pulverizing and grinding step 3 and be directly fed to the electroytic cell 5, in the flow sheet of FIG. 1. In this case, a chloride solution or silicofluoride solution may be used as the electrolytic solution.

Preferable embodiments of the electrolytic cell used for the practice of the method of this invention and the continuous electrolysis processes will now be explained by referring to FIGS. 2 to 5.

An embodiment of the electrolytic cell of this invention is illustrated in FIG. 2. In this embodiment, the electrolytic cell 10 is fixed on a base frame 30 to which vibration generators 31 and 32 are mounted to give a special composite vibration to the whole cell 10 and disperse seed particles in the electrolyte. This composite vibration consists of a circular vibration in the horizontal plane, i.e., a horizontal oscillation, and an upand-down vibration in the vertical plane. In this embodiment, in order to generate this composite vibration, an oscillating mechanism 31 comprising two or more eccentric cams, transmission means, reducing gears and a driving motor, and a vibrator 32 for generating a vertical vibration are used. In the oscillating mechanism, instead of the cam an optional member capable of generating a vibration by utilizing oil pressure may be used. Also in the vertical vibrator an optional device capable of generating a vertical vibration, such as a magnetic vibrator, a vibrator operated by an eccentric loading motor or a cam vibrator may be used. In this case, it is possible to increase the durability of the apparatus and reduce the driving energy, by fixing to the base frame 30 a spring member (not shown) such as sheet spring or coil spring and synchronizing the inherent vibration of the electrolytic cell inclusive of the base frame 30 .with the oscillating vibration and vertical vibration.

Inside the electrolytic cell 10 fixed on the base frame 30, a woven fabric is hung horizontally or with a slight gradient as diaphragm 11, by which the cell is divided into the lower cathode chamber 12 and the upper anode chamber 13. An anode plate 14 is spread through the bottom of the cathode chamber a an insoluble anode l5 ofa net of several mesh is spread in the anode chamber. In general, it is conceived that the use of a diaphragm is not preferred because it increases the electric resistance and increases the electric voltage between both electrodes. Accordingly in the conventional methods, only when the insoluble residue containing impurities is formed on the anode and floats in the electrolytic solution, the diaphragm is used to prevent such floating residue from contaminating the pure metal precipitated on the cathode. Also in this invention, the increase of the electric resistance caused by the diaphragm cannot be avoided, but when a woven fabric is used as the diaphragm, the degree of increase of the electric resistance is low. Further, in this invention the increase of the electric voltage, i.e., the electric power, caused by the use of the diaphragm is compensated by the following features; since the distance between diaphragm 11 and cathode plate 14 can be shortened to about 0.5 cm and the distance of diaphragm 11 an insoluble anode 15 can be shortened to about I cm, the distance between both electrodes can be extremely shortened, with the result that the electric resistance due to the electrolytic solution can be reduced; the electric resistance can be reduced according to need by elevating the temperature of the electrolytic solution; and since the electrolytic cell can be made compact and scalable, the escape or loss of the heat can be minimized and, therefore, no special heat source is required for heating the electrolyte or maintaining its temperature at a prescribed level. The use of the diaphragm l1 prevents the mingling of the electrolytic solution in the anode zone with that in the cathode zone, and increases the allowance of the type and amount of impurities of the crude metal fed to the anode zone. For these reasons, the use of the diaphragm in this invention does not need any special care or attention, as compared with the conventional electrolytic refining methods. Thus, in this invention, if particles of an intermediate material, a sulfide or a sulfide ore are charged in the anode chamber, the pure product is obtained similarly and the purity of the product is not influenced by the kind of starting particles.

It is not always necessary that the diaphragm should be hung horizontally in the electrolytic cell. When it is positioned with a slight gradient, bubbles in the cathode chamber can be excluded rather conveniently.

The zone positioned below the diaphragm ll, namely the cathode chamber 12, has generally a circular or rectangular cross-section. In the latter case, it is preferred that the four corners have a roundness of a curvature radius several times as great as that of the circle of the oscillating vibration generated by the abovementioned oscillating mechanism 31. In the case of either the circular or rectangular cross-section, it is preferred to provide a notched portion 16 in the side wall 23 at the end facing the cathode plate 14, whereby the current density in the peripheral portion of the cathode can be reduced and adherence of the metallic particles to the cathode can be prevented. The same effect can be attained by forming an insulating film on the surface of the peripheral portion of the cathode. In the cathode chamber 12, an outlet 18 for withdrawal of enlarged metal particles is provided at the bottom of the electrolyticcell in the position farthest from an electrolyte inlet 17 mounted on the side wall 23. Further, an auxiliary discharge outlet 19 is provided to withdraw a liquid to be used for repulping the starting material and to exclude bubbles from the cathode chamber. Since the thickness of the cathode chamber is generally small, the position of the inlet 17 is decided such that the electrolytic solution can be distributed uniformly throughout the cathode chamber. At the time when the starting electrolytic solution is charged from the inlet 17, seed particles contained in the starting electrolytic solution are repulped by means of a repulper 44 in FIG. 3.

The anode chamber 13 positioned above the diaphragm 11 has the same Cross-section as that of the cathode chamber and comprises a horizontal ceiling lid 20, an insoluble anode plate 15 spread close to the diaphragm 11, an electrolyte inlet 21 formed through the side wall below one end of the anode plate and made to open toward the anode chamber, and an outlet 22 for withdrawal of the electrolytic solution provided through the ceiling lid 20 in the position farthest from the inlet 21. When the electrolyte flows into the anode zone from the inlet 21, the starting particles are repulped and incorporated in the electrolyte. The distance between the ceiling lid 20 and diaphragm 11 can be shortened to about 1 cm and the ceiling lid can be utilized as the anode plate. But, in order to ensure the complete contact of particles of the crude metal with the anode, it is preferred to provide a net-like, insoluble anode 15 in the position several millimeters above the diaphragm.

In connection with the above embodiment of the electrolytic cell of this invention, the steps of the method of this invention, auxiliary devices attached to the main apparatus, and effects attained by this invention will be described by referring to FIGS. 2 and 3.

The outlet 22 of the anode chamber is connected with the inlet 17 of the cathode chamber by means of conduits via an impurity separator 40, a pump 41, an electrolyte reservoir 43 provided with an inlet for receiving the starting electrolyte, and a repulper 44. The term impurity separator" used herein is a generic term indicating a series of apparatus including a filtrator for removing solid impurities, a reaction tank for removing harmful ions, a tank for precipitating harmful ions, a filtrator for removing such precipitates, a solvent extraction device, etc. A suitable combination of these devices isselected depending on the kinds of impurities to be removed. The outlet 18 of the cathode chamber is connected with the electrolyte reservoir 43 by means of conduits via a separator 45. The separator 45 is provided to separate the product from the electrolytic solution and it is preferred to use a thickener, a press filter or a centrifugal separator as the separator 45. The separator 45 is connected with a drying machine by which the product separated in the separator 45 is dried.

The auxiliary discharge outlet 19 is connected with the inlet 21 of the cathode chamber by means of conduits via a pump 47 and a repulper 48. This recycle system need not always be provided, and it is possible to feed the starting particles directly from an inlet 24 provided on the ceiling lid of the electrolytic cell.

In the repulper 44 seed particles of the pure metal are repulped and the electrolytic solution containing the repulped seed particles flows into the cathode chamber 12 from the inlet 17 of the cathode chamber, in which electrolytic precipitation of the metal advances on the surface of the seed metal particles and their size is increased with the advance of the electrolytic precipitation. The apparatus of this embodiment is designed to effect the electrolysis efficiently in the case of seed particles of a size exceeding about 90 microns. Generally, the seed particle metal is the same as the metal to be precipitated and recovered, but it is not always necessary to use the same metal. The seed metal is prepared and formed into particles of a prescribed size by a customary electrolytic metal powder production process or a known method comprising spraying a molten metal. in order to disperse such seed metal particles on the surface of the cathode, a composite vibration is given to the entire electrolytic cell. The composite vibration consists of a horizontal oscillating vibration and a vertical up-and-down vibration and is generated by the vibration-generating mechanism. As the oscillating vibration a combination of one-dimensional movements made longitudinally and laterally in the horizontal plane according to the shape or size of the electrolytic cell may be used, but it is generally convenient to generate the oscillating vibration by a mechanical circular movement. The intensity of the composite vibration, i.e., the amplitude and cycle of the composite vibration, is an important factor for conducting the electrolysis stably. In case the intensity of the oscillating vibration is too great, metal particles tend to adhere to one another to form agglomerates of particles or in the peripheral portion of the cell adherence of metal particles on the electrode surface occurs, which results in the decrease of the particle concentration in the central portion and in the precipitation or deposition of the metal on the electrode surface. On the other hand, when the intensity of the oscillating vibration is too small, it is impossible to disperse the metal particles uniformly throughout the broad surface of the electrode because a deviation appears in the distribution of metal particles. When the vertical vibration is too intense, it sometimes happens that the metal is precipitated on the electrode surface, and when the vertical vibration is too weak, adherence of metal particles on the electrode surface or formation of agglomerated particles is caused to occur. And in each case, it is impossible to conduct the electrolysis operation stably. When these conditions are considered collectively, it is desirable that the composite vibration consists of an oscillating vibration of an amplitude (circle) of less than 30 mm and a frequency of 10 to 300 cycles per minute and a vertical vibration of an amplitude of less than 2 mm and a frequency of about l0 cycles per second to a commercial alternating current cycle (50 or 60 cycles per second). As is illustrated in examples given hereinbelow, under such vibration conditions the electrolysis can be performed while preventing adherence of metal particle to one another and precipitation of metal particles on the electrode surface. When the cathode chamber 12 has a rectangular cross-section, the electrolysis process may be carried out effectively by a method by which the direction of the up-and-down vibration is not strictly vertical but slightly inclined, so that inclined vibration metal particles are gradually forwarded in the horizontal direction toward the outlet 18 of the cathode chamber 12 while they are equally vibrated.

The lowering of the metal ion concentration caused in proportion to the advance of the electrolysis can be compensated by feeding the starting electrolyte of a high metal ion concentration to the cathode chamber from the inlet 17 of the cathode chamber. In this case, the reverse flow of the electrolyte from the anode chamber to the cathode chamber is prevented by maintaining the pressure of feeding electrolyte from the inlet 17 of the cathode chamber at a level a little higher than the pressure of withdrawing the electrolyte from the outlet 22 of the anode chamber. A part of the electrolyte contained in reservoir 43 is used for dispersing seed metal particles in the repulper 44 and feeding them continuously to the cathode chamber. The other part of the electrolyte flows from the reservoir 43 to the outlet 18 of the cathode chamber via separator 45. The so introduced electrolyte constitutes a suitable stream in the vicinity of the outlet 18 of the cathode chamber and is utilized for selectively withdrawing only metal particles of larger sizes capable of falling down against the stream from the outlet 18 of the cathode chamber. The particles thus withdrawn from the outlet 18 of the cathode chamber are separated from the electrolyte by means of the separator 45 and dried to an end product by means of the drying machine 46.

In the above-mentioned embodiment of the electrolysis apparatus, a great amount of the electrolyte is used for increasing the electrolysis efficiency. In principle, the electrolytic solution is fed from the cathode chamber to the anode chamber via the diaphragm, and the starting particles are repulped into the electrolytic solution withdrawn from the auxiliary outlet 19 in the repulper 48 and are continuously fed from the inlet 21. It is also possible to continuously feed the starting particles from the inlet 24 provided on the ceiling lid 20 of the anode chamber. The electrolyte having passed through the diaphragm 11 from the cathode chamber flows into the anode chamber 13, and the electrolyte contained the repulped starting particles, which has been introduced into the anode chamber 13 from the inlet 21, are combined in the anode chamber 13, and the metal ion concentration of the electrolyte is increased in the anode chamber 13 by the anodic reaction of the starting metal particles. Then the electrolytic solution of a high metal ion concentration flows out from the outlet 22 provided on the ceiling lid 20 together with fine insoluble residual materials derived from the impurities contained in the starting particles. The residues of impurities and ions of impurities are removed from the electrolytic solution by means of the impurity separator 40. Then the electrolytic solution from which the impurities have been removed is fed to the reservoir 43 by means of the pump 41.

As is seen from the explanation given hereinabove, the electrolytic cell of this invention has a configuration characterized by a very small height and a relatively large horizontal area. Accordingly, when -it is necessary use a plurality of electrolytic cells, if these cells are arranged horizontally, a broad floor area is required for the cells, which is undesirable from the economical viewpoint and inconvenient for the constructure of the plant. In order to solve this problem electrolysis apparatus of a pile type has been developed, which will now be explained by referring to FIG. 4. This apparatus is constructed of two or more piled electrolytic cells of this invention by utilizing the fact that the thickness ofthe electrolytic cell ofthis invention can be greatly reduced. As is illustrated in FIG. 4, a plurality of electrolytic cells A-l, A-2, A-3 are piled and the assembly of the piled cells is fixed by fixing frames 33 and base frame 30. The above-explained composite vibration is given to the base frame 30. In this embodiment, the outlet 22 of the anode chamber and the out let l8 ofthe cathode chamber should be provided vertically or almost vertically above or below the cell so as to conduct their functions completely. Accordingly, as is shown in the drawing, the electrolytic cells are positioned in a little staggered relationship to each other. Since tubes for feeding and withdrawing the electrolytic solution are connected in a parallel line with respect to each cell, it is preferred that electrodes of each cell are connected in a parallel line.

In this invention fine particles of the seed metal are grown to large metal particles in the cathode chamber of the electrolytic cell. However, the optimum condition of the composite vibration given to the electrolytic cell varies depending on the size of the particles in the cell, though the degree of the variation is not great. Accordingly, if it is intended to grow fine particles of the seed metal into larger particles by using only one electrolytic cell, a problem concerning stable operation is brought about. In order to solve this problem the multistage electrolysis system shown in FIG. 5 has been developed which comprises a plurality of electrolytic cells illustrated in FIG. 2 or electrolysis apparatus of a pile type illustrated in FIG. 4, or a combination of the cells of these two types. With respect to each electrolytic cell, tubes for feeding and discharge of metal particles are arranged in a series and tubes for flowing of the electrolyte and charging of the starting metal particles are arranged in a parallel fashion. More specifically. tubes for introducing starting particles and flowing electrolyte in and out are provided so that starting metal particles will be introduced into each unit apparatus individually and the electrolyte flows in and is withdrawn separately in each unit apparatus. On the other hand, tubes for feeding and discharging metal particles are arranged so that a tube for discharging metal particles of one unit apparatus is connected with a tube for feeding metal particles of the subsequent unit apparatus. Accordingly, seed particles travel through all unit apparatus in succession while being enlarged as the result of the electrolysis, though the direct flowing of the electrolyte from one unit apparatus to the subsequent unit apparatus is substantily inhibited. A vibrator mechanism is provided to each of the elecrolytic cells so that a composite vibration optimum to the cell will be imparted thereto. The metal particles prepared in the first-stage electrolytic cell are discharged from the outlet of the cathode chamber and introduced into the cathode chamber of the secondstage electrolytic cell from the inlet thereof. The joint portion connecting the outlet of the cathode chamber of the first-stage electrolytic cell with the inlet of the cathode chamber of the second-stage electrolytic cell for introducing the seed particles and electrolytic solution should comprise a separator connected with the outlet of the first-stage electrolytic cell and a repulper connected with the inlet of the second-stage electrolytic cell as well as a device for preventing the mingling and reverse flow of the electrolytic solution. More specifically, metal particles which have fallen down in the rising electrolytic solution from the outlet of the firststage electrolytic cell are deposited on the bottom of the separator and they, in the state packed in a conduit connected with the repulper positioned intermediate between the first-stage electrolytic cell and secondstage electrolytic cell, prevent almost completely the mingling of the electrolyte from the first-stage electrolytic cell with the electrolyte of the second-stage electrolytic cell and the reverse flow of the electrolyte of the second-stage cell toward the first-stage cell. The metal particles packed in the conduit are gradually fed to the repulper by the vibration given from the outside or by means of a screw member. It is not necessary to provide the repulper with a special agitating member, and a sufficient agitation can be attained by a turbulent flow caused by the introduction of the electrolytic solution. Since the seed particles have been grown to larger particles in the first-stage electrolytic cell, the conduit leading to the inlet of the cathode chamber of the second-stage electrolytic cell has a diameter smaller than that of the conduit leading to the inlet of the cathode chamber of the first-stage electrolytic cell so that the flow rate of the electrolyte introduced into the cathode chamber of the second-stage electrolytic cell will be higher than the flow rate of the electrolyte introduced EXAMPLE 1 Experiments were conducted to show that when metal particles are suspended in a catholyte, namely the electrolyte in the cathode zone, the electrolysis can be accomplished even by application ofa cathode current of a much higher density than that applicable in the conventional method.

Two liters of a solution containing Cu at a concentration of about 50 grams per liter and H 80, at a concentration of about 50 grams per liter were charged in a beaker. A cylinderical Saran cloth of 9 cm diameter was dipped into the beaker to form an outer anode zone and an inner cathode zone in the beaker. The liquid volumes of both zones were almost equal (about 1 liter). A cylinderical copper plate of an area of about 500 cm was used as the anode and two cylindrical copper plates of a height of 2 cm and a circumference of 18 cm were used as the cathode. The outer surface and periphery of each cathode copper plate was covered and insulated with an epoxy resin. The total area of the cathode was about 50 cm The electrolyte in the cathode zone was agitated by a screw rotating at about 800 r.p.m. and 50 g of copper particles, about 80 percent of which have a size finer than I mesh were suspended in the catholyte. In this state the electrolysis was conducted for 205 minutes by passing an electric current of 10 A. An apparent current density of the cathode was A/dm which is about 10 times as high as the current density adopted in the conventional electrolysis method (about 2 A/dm The amount of copper precipitated on the suspended copper particles was 33.3 g which corresponds to 83 percent of the stoichiometric amount. Formation of dendrites was not appreciably observed on the cathode plates. The amount of anode dissolved was 24.1 g and the voltage between both electrodes was in the range of from 1.1 to 2.0 volts.

The electrolysis was conducted under the same conditions as in the above experiment for 30 minutes by using an electric current of 20 A. The apparent current density on the cathode was 20 times as high as that in the conventional electrolysis. Formation of dendrites was not observed and the amount of precipitated copper was l 1.2 g, which corresponds to 95 percent of the stoichiometric amount. The voltage between both electrodes was 2.1 3.0 volts.

EXAMPLE 2 Experiments were conducted to show that when metal sulfide particles of a low electric conductivity are used as the starting metallic material, addition of a valency-changeable metal or particles of an electrically conductive substance to the electrolyte in the anode zone is effective for facilitating the delivery of electrons between the particles and anode and conducting the electrolysis efficiently.

A starting copper sulfide containing 70 percent of copper and 3 percent of iron was pulverized to particles of 200 mesh, and 90 g of the particles were suspended in 180 ml of 2N sulfuric acid. The suspension was charged into the cathode zone partitioned by a Saran cloth from the cathode zone. The electrolysis was conducted under agitation while passing an electric current of 8 A. The anode was a copper plate having the total area (both faces) of 40 cm Results are shown in Table 1 below.

TABLE 1 Anode Current Efficiency (71) With respect to copper dissolved 36.4 in anode zone With respect to iron dissolved in 9.] anode zone Total 45.5

The electrolysis was conducted under the same conditions as in the above experiment by using the same starting metal sulfide particles and adding the ferrous ion to 180 ml of 2N sulfuric acid at a concentration of 10 grams per liter. Results are shown in Table 2 below.

TABLE 2 Anode Current Efficiency (71) With respect to copper dissolved 84.3 in anode zone With respect to iron dissolved in 6.5 anode zone Total 90.8

The electrolysis was conducted under the same conditions as above by throwing 30 g of lead metal particles of mesh into the anode zone. Results are shown in Table 3 below.

TABLE 3 Anode Current Efficiency (7!) With respect to copper dissolved 75.0 in anode zone With respect to iron dissolved in 7.6 anode zone Total 82.6

In the first experiment where the delivery of electrons between the particles and anode was insufficient, the current efficiency was low and formation of oxygen gas was observed. But in the second and third experiments where the electrolysis was conducted by addition of the ferrous ion or metal lead particles, the current efficiency was high and formation of oxygen gas was not observed.

EXAMPLE 3 400 grams of pure copper particles of mesh were suspended in 300 ml of 1N sulfuric acid containing copper sulfate at a concentration of 200 grams per liter, and the suspension was fed into the cathode zone partitioned by a Saran cloth from the anode zone. The electrolysis was conducted by passing an electric current of 8 A under agitation by means of an up-anddown vibrating perforated plate. The cathode was made up of a copper plate having the surface area of 15.1 cm'. Results are shown in Table 4 below.

copper cathode From the results shown in Table 4 it is seen that the electrolysis of copperis effected on the surface of the seed particles.

EXAMPLE 4 180 ml of 1N HCl containing the ferric ion at a concentration of grams per liter were charged in the anode zone partitioned by a Saran cloth from the cathode zone. 40 grams of starting lead sulfide particles of 200 mesh containing 83 percent of lead and 12 percent of sulfur were added to the l-lCl solution and the electrolysis was conducted at 68C. under agitation while passing an electric current of 4A with use of a carbon anode having the surface area of 17.9 cm and a cathode composed of a lead plate. The anode current efficiency with respect to the lead dissolved in the anode zone was 80.7 percent.

EXAMPLES 200 grams of pure lead particles of 200 mesh were suspended in 180 ml of a lead chloride solution containing lead at a concentration of 67 grams per liter, and the suspension was charged into the cathode zone partitioned by a Saran cloth from the anode zone. The electrolysis was conducted at 68C. under agitation while passing an electric current of 4 A with use of a carbon anode having the surface area of 80 cm and a lead plate cathode having the surface area of 18.9 cm A predetermined amount of lead chloride was supplied at predetermined intervals. Results are shown in Table 5 below.

TABLE 5 Amount Increased Cathode Current The experiment was conducted with use of the electrolytic cell illustrated in FIG. 2.

The cell had a circular cross-section, and the inner diameter at the position of the diaphragm was 12.0 cm. The height of the cathode chamber was 1.3 cm and the height of the anode chamber was 1.3 cm. The distance between both electrodes was about 2.6 cm. The starting electrolyte containing copper sulfate in an amount of about 50.7 grams per liter calculated as copper ion and a small amount of sulfuric acid was fed to the cathode chamber at a flow rate of about 57 to about 60 ml/min, and the same amount of the electrolyte was discharged from the anode chamber. The electrolysis was conducted at C. while passing an electric current of 60 A.

400 grams of copper particles of 48 65 mesh were fed to each of the cathode and anode chambers, respectively. The up-and-down vibration was made constant at an amplitude of 0.5 mm and a frequency of 1,440 cycles per minute, and the influence caused by the horizontal oscillating vibration of an amplitude of 2.5 cm and a frequency of cycles per minute was examined. Results are shown in Table 6 below.

TABLE 6 Cathode Current Efficiency (1' Horizontal oscillating with respect to with respect to cathode vibration copper particles plate not given about 30 given 95.8 0.46

The cathode current efficiency means the ratio of the current used for the electrolysis to the total current fed. Accordingly, the fact that the cathode current efficiency with respect to the cathode plate was as high as 30 percent indicates that the cathode plate was enlarged in a short period of time and the electrolysis could not be conducted stably.

EXAMPLE 7 TABLE 7 Cathode Current Efficiency (71) Amplitude of vertical vibration (mm) with respect to with respect to cathode copper particles plate 0 electrolysis was impossible because of formation of agglomerated particles 0.3 95.1 0.00 0.5 95.8 0.46 1.0 82.9 13.2 2.0 84.4 10.6

From the results shown in Table 7, it is seen that in the case of copper particles of 48 65 mesh a most preferable vibration to be imparted to the electrolytic cell is a composite vibration consisting of a horizontal oscillating vibration of an amplitude of 2.5 cm and a frequency of 180 cycles per minute and a vertical upand-down vibration of an amplitude of 0.3 mm and a frequency of 1,440 cycles per minute.

EXAMPLE 8 Example 7 was repeated while imparting the most suitable vibration found in Example 7 to the electrolytic cell and varying the amount of copper particles added to the cathode chamber to examine the influence of the amount of copper particles on the electrolysis. Results are shown in Table 8 below.

TABLE 8 Cathode Current Efficiency (Z) Amount added of with respect to with respect to cathode copper particles (g) copper particles plate EXAMPLE 9 The electrolysis was conducted for a long time at an average temperature of 797C. while passing an electric current of 60 A under the optimum conditions determined by experiments of Examples 6, 7 and 8, namely under the conditions imparting to the electrolytic cell a composite vibration consisting of a horizontal oscillating vibration of an amplitude of 2.5 cm and a frequency of I80 cycles per minute and a vertical upand-down vibration of an amplitude of 0.3 mm and a frequency of 1,440 cycles per minute. The following results were obtained.

Voltage between electrodes: [.9 2.4 volts Copper ion concentration (under stationary operation): 32.0 g in the cathode chamber 51.8 g in the anode chamber Cathode current efficiency: 93.3 percent with respect to copper particles less than 0.0l percent with respect to the cathode plate Anode current efficiency: 99.8 percent Size of copper particles in the cathode chamber:

before the electrolysis 48 65 mesh 100% after the electrolysis 4865mesh-0% 3248mesh0% 24 32 mesh about IO 7c 14 24 mesh about 90 What we claim is:

l. A method for the aqueous electrolytic precipitation of a metal as particles from a starting material selected from a crude metal of zinc, iron, cobalt, nickel, tin, lead, and copper and sulfides thereof, using at least one electrolytic cell having an anode zone and a cathode zone each containing an electrolyte solution, which comprises introducing particles of the starting material into said anode zone having an anode and introducing seed particles into said cathode zone having a cathode, said cathode zone being separated from said anode zone by a water-permeable diaphragm, the particles of starting material and seed particles being kept in the suspended state by agitation and by passing an electric current through said anode and cathode, the particles of the starting material being positively charged due to collision with the anode and are dissolved in an electrolyte solution, the seed particles being negatively charged due to collision with the cathode and the metal ions in the electrolyte solution are cathodically precipitated as the metal on said seed particles, the seed particles being of the pure metal.

2. The method of claim I, wherein electrolyte solution is continuously fed into the cathode zone so that the hydrostatic pressure in said cathode zone is maintained at a level higher than the hydrostatic pressure in said anode zone, to thereby prevent the migration of soluble and insoluble impurities contained in the starting material from said anode Zone into said cathode zone through said diaphragm, and said impurities are continuously discharged together with the electrolyte solution discharged from said anode zone.

3. The method of claim 2, wherein the impurities are removed from the discharged electrolyte solution containing the impurities and clarified electrolyte solution from which the impurities have been removed is recycled to said cathode zone.

4. The method of claim 1, wherein said starting material is a metal sulfide ofa low electric conductivity and at least one member selected from ferric and cupric ions capable of accepting an electron from said metal sulfide and donating it to the anode is present in the electrolyte solution in said anode zone.

5. The method of claim 1, wherein said particles of starting material and seed particles of the pure metal are continuously fed into said anode zone and cathode zone, respectively, and coarse particles formed by the cathodic precipitation of the metal onto said seed particles are continuously withdrawn as the product.

6. The method of claim 1, wherein said particles of starting material and seed particles are suspended in the electrolyte solution by imparting vertical and horizontal vibrations to the electrolyte solution.

7. A method for the aqueous electrolytic precipitation ofa metal as particles from an electrolyte solution containing ions of the metal selected from zinc, iron, cobalt, nickel, tin, lead, and copper as a salt dissolved therein, which comprises introducing particles of an insoluble metal into an anode zone of an electrolytic cell having an insoluble anode and introducing seed particles and the electrolyte solution containing the metal ions to be precipitated into a cathode zone of said electrolytic cell having a cathode, wherein said cathode zone is separated from said anode zone by a waterpermeable diaphragm, said particles of an insoluble metal and seed particles being kept in the suspended state by agitation and by passing an electric current through said anode and cathode, the particles of said insoluble metal being positively charged due to collision with said anode and the liberation of oxygen gas takes place at the surface of said insoluble metal particles, said seed particles being negatively charged due to collision with said cathode and the metal ions in the electrolyte solution are cathodically precipitated as the metal onto said seed particles, the seed particles being of the pure metal.

8. The method of claim 7, wherein said seed particles of the pure metal are continuously fed into the cathode zone, and coarse particles formed by the cathodic precipitation of the metal on said seed particles are continuously withdrawn as the product.

9. The method according to claim 7, wherein said particles of an insoluble metal and seed particles are suspended in the electrolyte solution by imparting vertical and horizontal vibrations to the electrolyte solution. 

2. The method of claim 1, wherein electrolyte solution is continuously fed into the cathode zone so that the hydrostatic pressure in said cathode zone is maintained at a level higher than the hydrostatic pressure in said anode zone, to thereby prevent the migration of soluble and insoluble impurities contained in the starting material from said anode zone into said cathode zone through said diaphragm, and said impurities are continuously discharged together with the electrolyte solution discharged from said anode zone.
 3. The method of claim 2, wherein the impurities are removed from the discharged electrolyte solution containing the impurities and clarified electrolyte solution from which the impurities have been removed is recycled to said cathode zone.
 4. The method of claim 1, wherein said starting material is a metal sulfide of a low electric conductivity and at least one member selected from ferric and cupric ions capable of accepting an electron from said metal sulfide and donating it to the anode is present in the electrolyte solution in said anode zone.
 5. The method of claim 1, wherein said particles of starting material and seed particles of the pure metal are continuously fed into said anode zone and cathode zone, respectively, and coarse particles formed by the cathodic precipitation of the metal onto said seed particles are continuously withdrawn as the product.
 6. The method of claim 1, whereiN said particles of starting material and seed particles are suspended in the electrolyte solution by imparting vertical and horizontal vibrations to the electrolyte solution.
 7. A method for the aqueous electrolytic precipitation of a metal as particles from an electrolyte solution containing ions of the metal selected from zinc, iron, cobalt, nickel, tin, lead, and copper as a salt dissolved therein, which comprises introducing particles of an insoluble metal into an anode zone of an electrolytic cell having an insoluble anode and introducing seed particles and the electrolyte solution containing the metal ions to be precipitated into a cathode zone of said electrolytic cell having a cathode, wherein said cathode zone is separated from said anode zone by a water-permeable diaphragm, said particles of an insoluble metal and seed particles being kept in the suspended state by agitation and by passing an electric current through said anode and cathode, the particles of said insoluble metal being positively charged due to collision with said anode and the liberation of oxygen gas takes place at the surface of said insoluble metal particles, said seed particles being negatively charged due to collision with said cathode and the metal ions in the electrolyte solution are cathodically precipitated as the metal onto said seed particles, the seed particles being of the pure metal.
 8. The method of claim 7, wherein said seed particles of the pure metal are continuously fed into the cathode zone, and coarse particles formed by the cathodic precipitation of the metal on said seed particles are continuously withdrawn as the product.
 9. The method according to claim 7, wherein said particles of an insoluble metal and seed particles are suspended in the electrolyte solution by imparting vertical and horizontal vibrations to the electrolyte solution. 